The invention refers to the field of reproduction technology and is directed to an apparatus for deflecting an optical beam. The apparatus is essentially designed as a prism and has an entry face as well as at least one reflection face and an exit face.
Devices for deflecting optical radiation are employed, for example, in originals scanner devices or in recording devices.
In an originals scanning device, also referred to as an input scanner, a light beam is conducted line-by-line with a light deflector across an original to be scanned, and wherein the scan light reflected by the original or transmitted through the original is converted into an image signal in an opto-electronic converter. In a recording device, also referred to as a recorder, an exposer or an output scanner, a light beam for recording information is intensity-modulated by an image signal and is conducted line-by-line across a light-sensitive recording material with a beam deflector.
When the scanning or recording device is designed as a flat bed device, the holder for the original or for the recording material is a planar surface across which the light ray is deflected line-by-line, and that moves relative to the light deflector perpendicularly relative to the deflection plane.
When the scanning or recording device is designed as an inside drum device, the holder for the original or for the recording material is a non-rotational inside drum designed like a cylindrical segment. The light deflector moves relative to the inside drum parallel to its longitudinal axis, and the light beam is radially deflected across the inside surface of the inside drum perpendicularly to the longitudinal axis.
For example, U.S. Pat. No. 3,875,587 discloses an apparatus for deflecting an optical beam in an inside drum recording device. The apparatus therein is designed as a pentaprism. The pentaprism that rotates around the longitudinal axis moves across the inside drum in the axial direction, as a result whereof a recording beam that is modulated with the information to be recorded and proceeds parallel to the inside drum axis is perpendicularly deflected onto the inside surface of the inside drum line-by-line by the pentaprism.
A pentaprism has no pyramid errors such as, for example, a polygonal mirror, and is insensitive to small rotations around the axis perpendicular to the principal section, so that the recording beam is deflected by exactly 90.degree., even given an angular wobble that arises due to tolerances in the region of the bearing for the pentaprism. A good recording quality is in fact achieved by employing a pentaprism as a beam deflector; one disadvantage, however, is that respectively only one line can be recorded per revolution of the pentaprism. As a consequence of the relatively poor degree of utilization per revolution (duty cycle) of the pentaprism, thus only a low recording speed can be achieved.
Another device for deflecting an optical beam in an inside drum recording apparatus is disclosed by EP-A-0 354 028. Given the rotating prism recited therein, two recording beams are generated having an offset of approximately 180.degree., as a result whereof two lines can be recorded on the recording material per revolution of the prism. The recording speed can in fact be enhanced with this apparatus. However, it has the disadvantage that an angular wobble is doubled, and thus the recording quality is substantially reduced.
Another apparatus for beam deflection is disclosed by WO 90/15355. In order to alleviate the influences of disturbances, two reflection faces are arranged herein the region of a rotating shaft, the first reflection face thereof facing toward a beam source deflecting the light ray in the direction onto the second reflection face and the latter aligning the light ray onto a material to be exposed. This apparatus has the disadvantage that only one line per revolution can again be exposed on the recording material. An angular wobble is completely suppressed in this apparatus.
U.S. Pat. No. 4,875,720 recites different prism shapes that completely suppress angular wobble, but do not allow the production of two recording beams.
It is not possible with the assistance of the known apparatus to realize a beam deflector such that it is both simply constructed in structural terms and also guarantees a qualitatively high-grade transmission of an optical beam. In particular, the known apparatus are not in the position to undertake a reduction of an angular wobble to an adequate extent.